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Chilly lifeforms The discovery of bacteria living in cold and salty water deep in an Antarctic lake suggests that microbes could exist in extreme conditions on other worlds, say US researchers.

Professor Peter Doran of the University of Illinois and colleagues found the bacteria after analysing water samples taken from Lake Vida in the Antarctic.

The uncomfortably briny water, registering a chilly -13°C, is sandwiched between a 16-metre thick layer of ice and a layer of permafrost below that is almost 1 kilometre deep, according to their report in the Proceedings of the National Academy of Sciences.

Despite the hostile conditions the scientists found an ecosystem with 32 different species of bacteria living deep under the ice.

Speaking from his camp in Antarctica, Professor Doran explains that the water trapped under the ice in the lake is completely isolated from the outside world. Water and air cannot get in or out and light cannot penetrate through the ice to that depth.

He says this raises the question of how the bacteria get their energy to survive, since photosynthesis is out of the question.

Doran believes the source is most likely to be hydrogen being produced by chemical reactions between the brine and the dolerite rock underlying and surrounding the lake.

"It's the reaction of the brine with that dolerite that's generating hydrogen and hydrogen is the energy source for the system. It's like a little fuel cell," he says.

"This is one of the few examples of a place where you have a completely closed system," says Doran. "There's no new materials delivered - it's sealed off. Because rates of metabolism are so slow - it's so cold and things are moving so slowly down there - it could last for a long time."

The water has been trapped for at least 2800 years and possibly longer, he says.

Microbes on Mars, Europa

"Where you find water you find life," says Doran. "The more and more we look we find that life can get an edge just about anywhere as long as there's water around."

Doran says that the work extends the boundaries of where life can exist and this may apply to planets and moons, such as Mars or Europa.

"A system like this on Mars could be covered over by wind-blown sediment and the ice wouldn't melt. The system would just stay buried down there, encapsulated," he says.

"Potentially you could have had something like this on Mars and it's buried now."

"For moons like Europa where you have a thick ice shell and you need some energy source for microbes to live underneath that shell, then this would be a small-scale model for that."

Dr Gene Tyson of the University of Queensland, who was not involved in the research, agrees that the work expands our ideas as to what life might look like on other worlds.

"We are starting to realise that if there's a way to make a living through basic chemistry then microorganisms are going to find a way to do it," says Tyson.

"We've got so many examples here on Earth where microorganisms live at the extremes of pH, temperature, pressure ... if any form of life exists outside of our planet then it's going to be microorganisms."